In a LTE (Long Term Evolution) scheme, an OFDMA (Orthogonal Frequency Division Multiple Access) scheme is used as a downlink radio access scheme, and a SC-FDMA (Single-Carrier Frequency Division Multiple Access) scheme is used as an uplink radio access scheme.
The OFDMA scheme is a multi-carrier transmission scheme where a frequency band is segmented into multiple narrower frequency bands (subcarriers) and data is transmitted in the individual subcarriers. According to the OFDMA scheme, faster transmission and improved frequency utilization efficiency can be achieved by densely arranging the subcarriers orthogonally to a frequency axis.
The SC-FDMA scheme is a single-carrier transmission scheme where a frequency band is segmented and different frequency bands are assigned to mobile stations for data transmission. According to the SC-FDMA scheme, since variations of transmit power can be suppressed, power consumption of the mobile stations can be reduced.
In the LTE scheme, the maximum transmit power available for a mobile station for uplink transmission is basically determined based on power capability of the mobile station, an assigned resource block, an applied modulation scheme, adjacent carrier interference and so on. Specifically, each mobile station determines the maximum transmit power Pcmax available for uplink transmission within the range of Pcmax_L<Pcmax<Pcmax_H. Here, the lower bound Pcmax_L and the upper bound Pcmax_H are defined as follows,Pcmax_L=Min{PEMAX−ΔTc,PPowerClass−(MPR+A-MPR)−ΔTc},andPcmax_H=Min{PEMAX,PPowerClass},respectively,
where PEMAX represents the maximum transmit power of the mobile station indicated from the network side, ΔTc represents an allowable reduction amount in use of resource blocks in band edges, and PPowerClass represents the maximum transmit power that should be provided to the mobile station. Also, MPR (Maximum Power Reduction) represents an allowable reduction amount determined based on the modulation scheme (such as QPSK) and the number of resource blocks, and A-MPR (Additional Maximum Power Reduction) represents an allowable reduction amount to avoid giving interference to adjacent systems.
The maximum transmit power Pcmax of the mobile station is determined within the range between the calculated lower and upper bounds Pcmax_L and Pcmax_H, and actual transmit power is determined such that it cannot exceed the maximum transmit power Pcmax.
Also, standardization for a LTE-Advanced scheme, which is a development of the LTE scheme, is currently being promoted in a standardization organization 3GPP (3rd Generation Partnership Project). In the LTE-Advanced scheme, a Carrier Aggregation (CA) technique will be introduced to achieve a higher throughput than the LTE scheme while keeping backward compatibility with the LTE scheme. In the CA, multiple LTE carriers called component carriers (CCs) are simultaneously used in communication. In the LTE-Advanced scheme using the CA, the maximum transmit power Pcmax, c is determined for each CC, and actual transmit power is determined for the CC such that it cannot exceed the maximum transmit power Pcmax, c.
Meanwhile, it is known that electromagnetic waves transmitted from a mobile station may affect the human body. In general, a Specific Absorption Rate (SAR) is used as an indicator indicative of an amount of energy to which the human body has been subjected from an electromagnetic wave emitting device for a certain time period, and the SAR acceptable for the human body is specified.
For example, see 3GPP TS 36.101 and 3GPP TS 36.213.